"The point is that it was a unit trust. So the money it had was other people's money on which they pay tax. If you were a United Kingdom owner of these things you paid income tax on your dividends and you paid tax in the normal way. If you were a foreigner you would pay tax in your own country."

He added that there are thousands of unit trusts and millions of people who own shares in Britain, many of whom hold them through unit trusts.

Cameron said he sold 5,000 units in the trust, which he owned jointly with his wife Samantha, in January 2010, before he became Prime Minister, for around £30,000.